The present invention relates to novel 5,6,7,8-tetrahydro-imidazo[1,5-a]pyrazine derivatives of formula (I) and their use as pharmaceuticals. The invention also concerns related aspects including processes for the preparation of the compounds, pharmaceutical compositions containing one or more compounds of formula (I), and especially their use as orexin receptor antagonists.
Orexins (orexin A or OX-A and orexin B or OX-B) are novel neuropeptides found in 1998 by two research groups, orexin A is a 33 amino acid peptide and orexin B is a 28 amino acid peptide (Sakurai T. et al., Cell, 1998, 92, 573-585). Orexins are produced in discrete neurons of the lateral hypothalamus and bind to the G-protein-coupled receptors (OX1 and OX2 receptors). The orexin-1 receptor (OX1) is selective for OX-A, and the orexin-2 receptor (OX2) is capable to bind OX-A as well as OX-B. Orexins are found to stimulate food consumption in rats suggesting a physiological role for these peptides as mediators in the central feedback mechanism that regulates feeding behaviour (Sakurai T. et al., Cell, 1998, 92, 573-585). On the other hand, it was also observed that orexins regulate states of sleep and wakefulness opening potentially novel therapeutic approaches to narcolepsy as well as insomnia and other sleep disorders (Chemelli R. M. et al., Cell, 1999, 98, 437-451).
Orexin receptors are found in the mammalian brain and may have numerous implications in pathologies as known from the literature.
Up to now, some low molecular weight compounds are known having a potential to antagonise either specifically OX1 or OX2, or both receptors at the same time. In WO01/85693, Banyu Pharmaceuticals claimed N-acyltetrahydroisoquinoline derivatives.
Other orexin receptor antagonists such as novel benzazepine derivatives are disclosed in WO02/051838. Pyrazolo-tetrahydropyridine derivatives as orexin receptor antagonists are known from WO07/122,591.
Furthermore, the use of solution-phase chemistry for the lead optimization of 1,2,3,4-tetrahydroisoquinoline derivatives as potential orexin receptor antagonists has been reported (Chimia, 2003, 57, 270-275).